Production of anhydrous sodium sulphate



Patented Sept. 13, 1938 2,129,813

PRODUCTION or ANHYDROUS SODIUM [SULPHATE Robert Roger Bottoms, Louisville, Ky., assignor to The Girdler Corporation, Louisville, Ky., a corporation of Delaware No Drawing. Application February 25, 1935, Serial No. 8,059

7 Claims. (01. 23-421) The present invention is a simple method of sulphate'solution, which may be a solution from obtaining anhydrous sodium sulphate directly which the hydrocyanic acid has been recovered from aqueous solutions of sodium sulphate, and in the treatment of coke oven gases or salt cake the main objects are to obtain the anhydrous from the manufacture of hydrochloric acid or a t salt in fine crystalline form, and to prevent the natural brine or extract, a salt of an alkali metal caking and adhering of the salt on the walls of or of magnesium which has a substantially the vessel in which the solution is treated. greater solubility in water than sodium sulphate. Although the invention of the present appli- Among the preferred salts which may be utication is broadly directed to the production of lized for this purpose are sodium thiocyanate,

l anhydrous sodium sulphate from aqueous solusodium, potassium or magnesium bromides or 10 tions of various concentrations and compositions, iodides, sodium or potassium thiosulphate, pothe invention Will be illustratively described in tassium or sodium formate, potassium thioconnection with the recovery of sodium sulphate cyanate and other highly soluble salts of metals from solutions which are produced in the rewhich do not form a precipitate with sulphuric l5 moval and recovery of hydrocyanic acid from acid, provided such salts have a greater solubility l5 coke oven gases. in Water than sodium sulphate. Of these com- In the process of removing hydrocyanic gases pounds I prefer to use sodium thiosulphate or from coke oven gases, or other gas mixtures consodium thiocyanate. taining the same, the gases are passed into con- The sodium sulphate solution with such additact with, or into absorption relationship with, tion may be evaporated and crystallized in ordi- 20 sodium sulphide solutions. nary tubular evaporators and crystallizers With The hydrocyanic acid will be absorbed by the out difiiculty due to caking and encrusting of the sodium sulphide with the production of sodium anhydrous sodium sulphate. The sodium sulthiocyanate which may then be oxidized to prophate will crystallize from the boiling solution in duce hydrocyanic acid and sodium sulphate. fi regular crystals which do t agg10merate 25 Af the v l n h r v y f hydro- It has been found that only a small proportion cyanic acid, the sodium sulphate will remain, and of such Mk metal or magnesium Salt is it is necessary for the econom1cal performance of quj red For examine, Such m need only be the process that such sodium sulphate be readded in amounts t exceeding 20% and t,

coveredso that it may be readily reconverted less than 1% and preferably between about 5% 30 mm sodium u1ph1de' to 10% of the amount of sodium sulphate present. However rcoverme this Sodlum sulphate The crystals resulting from a crystallization for reconversion into sodium sulphide, considerof Sodium Sulphate from Solutions con-taming able difficulty has been experienced in evaporatdium thiocyanate or other added Salts of 35 itfiittl ififplilfiftfie ti ttt tifitliiftfig aaaam alkali aaaaala may aaaa ha aaaaaaaaa salt tends to deposit upon and stick to the tubes fltom mother hquor and Wished flree i of the evaporators, which results in caking and mum thlocyanate or other ad ed 53 ts with encrusting of such tubes with loss in efiiciency Small amount of to and rapid breakdown of such mechanical equip- Havmg thus descr lbed my mventlon, What'I t, claim as new and desire to secure by Letters Pat- It is among the objects of the present invention @1113 S1 to provide a process which will permit the crys- 1. The process of producing anhydrous sodium tallization of anhydrous sodium sulphate while sulphate from a boiling water solution and in a concentrating a boiling aqueous solution conform which does not crystallize on or cling to the taining the same, with elimination of any tendequipment employed, said process including conency to cause encrusting or caking on the tubes centrating the solution by boiling to a point beof the evaporators which may be employed for yond which the sodium sulphate begins to be crysthis purpose, and without the need of cooling the tallized out of solution and adding to said solution, 0 solution or of adding excessive amounts of any before or during the boiling, a compound selected 5 foreign material. from the group consisting of sodium thiocyanate, Other objects will appear during the course of sodium thiosulphate, sodium formate, potassium the following specification. thiocyanate, potassium thiosulphate, potassium In accomplishing these objects it has been formate, sodium bromide, sodium iodide, potassifound most satisfactory to add to the Sod um um bromide, potassium iodide, magnesium bro- 55 mide, magnesium iodide, and in an amount between 1% and 20% of the sodium sulphate.

2. The process of 3. The process of producing anhydrous sodium sulphate or during the boiling.

5. The sulphate or during the boiling.

7. The process of producing anhydrous sodium sulphate from a boiling water solution and in a or during the boiling.

ROBERT ROGER BOTTOMS. 

